Electrophoretic particles and production process thereof

ABSTRACT

Electrophoretic particles are constituted by pigment particles provided with a polymer chain connected with a polymerization initiation group at a surface of pigment particle. The resultant electrophoretic particles are excellent particle size uniformity and dispersibility.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to electrophotographic particlescomprising pigment particles and a process for producing theelectrophoretic particles.

In recent years, with development of information equipment, the needsfor low-power and thin display devices have grown, so that extensivestudy and development have been made on display devices fitted to theseneeds.

As one of the display devices, there is an electrophoretic displaydevice.

In the electrophoretic display device, a multiplicity of electrophoreticparticles which are positively charged and colored are dispersed in aspace between a pair of substrates, each provided with anelectrode,together with an electrophoretic dispersion liquid which isfilled in the space and colored a color different from the color of theelectrophoretic particles. In the space, a partition wall is formed sothat it divides the space into a multiplicity of pixels along a planardirection of the substrates. By forming such a partition wall, it ispossible to define the space between the pair of substrates whilepreventing localization of the electrophoretic particles.

In such an electrophoretic display device, when a positive-polarityvoltage is applied to an observer's side electrode and anegative-polarity voltage is applied to an electrode on an oppositeside, the positively charged electrophoretic particles are collected soas to cover the opposite side electrode, so that a color identical tothe color of the electrophoretic dispersion medium is displayed when theelectrophoretic display device is observed from the observers side.

On the other hand, when a negative-polarity voltage is applied to theobserver's side electrode and a positive-polarity voltage is applied tothe opposite side electrode, the positively charged electrophoreticparticles are collected so as to cover the observer's side electrode, sothat a color identical to the color of the electrophoretic particles isdisplayed when the electrophoretic display device is observed from theobserver's side.

By performing such a drive of the electrophoretic display device on apixel-by-pixel basis, any image or character is displayed by amultiplicity of pixels.

With respect to a production process of the particles, several proposalshave been mode (Japanese Laid-Open Patent Application (JP-A) Tokkai2003-212913, JP-A Tokuhyo Hei 9-508216, and U.S. Pat. No. 6,194,488).

However, as the electrophoretic particles for use in the electrophoreticdisplay device, further improvements in uniformity of particle size anddispersibility have been required.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a process, forproducing electrophoretic particles, having solved the above describedproblems.

A specific object of the present invention is to provide electrophoreticparticles excellent in uniformity of particle size and dispersibility.

Another object of the present invention is to provide a process forproducing the electrophoretic particles and an electrophoretic displaydevice using the electrophoretic particles.

(1) First Invention

According to a first aspect of the present invention, there is providedelectrophoretic particles comprising pigment particles,

wherein at a surface of pigment particle, a polymer chain is connectedwith a nitroxide-mediated polymerization initiation group.

According to a first aspect of the present invention, there is provideda process for producing electrophoretic particles comprising pigmentparticles, comprising:

a step of introducing a nitroxide-mediated polymerization initiationgroup to a surface of pigment particle by reacting pigment particleshaving a function group, which is capable of reacting with a precursorof the nitroxide-mediated polymerization initiation group, with theprecursor of the nitroxide-mediated polymerization initiation group, and

a step of grafting a polymer chain to the nitroxide-mediatedpolymerization initiation group by nitroxide-mediated polymerization.

In a preferred embodiment, the precursor of the nitroxide-mediatedpolymerization initiation group is triethoxysilyl group, trimethoxysilylgroup or trichlorosilyl group.

Further, the function group which is capable of reacting with theprecursor of the nitroxide-mediated polymerization initiation group maypreferably be hydroxyl group.

(2) Second Invention

According to a second aspect of the present invention, there is providedan electrophoretic particles comprising pigment particles,

wherein at a surface pigment particle, a polymer chain is connected witha living radical polymerization initiation group and the polymer has anaffinity for a hydrocarbon solvent.

According to the second aspect of the present invention, there is alsoprovided a process for producing electrophoretic particles comprisingpigment particles, comprising:

a step of forming a living radical polymerization initiation group at asurface of pigment particle, and

a step of providing the pigment particles with a polymer chain connectedwith the living radical polymerization initiation group by livingradical polymerization,

wherein the polymer has an affinity for a hydrocarbon solvent.

According to the second aspect of the present invention, there isfurther provided a process for producing electrophoretic particlescomprising pigment particles, comprising:

a step of forming a nitroxide-mediated polymerization initiation groupat a surface of pigment particle by reacting pigment particles eachhaving hydroxyl group at a surface thereof with a precursor of thenitroxide-mediated polymerization initiation group, and

a step of polymerizing a monomer having an affinity for a hydrocarbonsolvent by nitroxide-mediated polymerization and providing the pigmentparticles with the resultant polymer connected with thenitroxide-mediated polymerization initiation group.

According to the second aspect of the present invention, there is stillfurther provided a process for producing electrophoretic particlescomprising pigment particles, comprising:

a step of forming a atom transfer radical polymerization initiationgroup at a surface of pigment particle by reacting pigment particleseach having hydroxyl group at a surface thereof with a precursor of theatom transfer radical polymerization initiation group, and

a step of polymerizing a monomer having an affinity for a hydrocarbonsolvent by atom transfer radical polymerization and providing thepigment particles with the resultant polymer connected with the atomtransfer radical polymerization initiation group.

The above described electrophoretic particles according to the first tothird aspects of the present invention are excellent in particle sizeuniformity and dispersibility.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are schematic sectional views showing an embodimentof an electrophoretic display device using electrophoretic particles ofthe present invention.

FIGS. 2(a) and 2(b) are schematic views showing a display example of theelectrophoretic display device.

FIG. 3(a) and 3(b) are schematic views showing another display exampleof the electrophoretic display device.

FIGS. 4(a) and 4(b) are schematic sectional views showing anotherembodiment of an electrophoretic display device using electrophoreticparticles of the present invention.

FIGS. 5(a) and 5(b) are schematic views showing a display example of theelectrophoretic display device of the another embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) EmbodimentsAccording to First Invention

In an embodiment according to the first aspect of the present inventionelectrophoretic particles are prepared by introducing anitroxide-mediated polymerization initiation group to a surface ofpigment particle and grafting a polymer chain from thenitroxide-mediated polymerization initiation group throughnitroxide-mediated polymerization.

(Introduction of Nitroxide-Mediated Polymerization Initiation Group)

Hereinbelow, a step of introducing the nitroxide-mediated polymerizationinitiation group to the surface of pigment particle will be described.

In accordance with a reaction formula (1-I) shown below, it is possibleto introduce the surface of pigment particle. More specifically, in areaction solvent, the pigment particles and Precursor 1 (shown below) ofthe nitroxide-mediated polymerization initiation group are added andreacted with each other to introduce the nitroxide-mediatedpolymerization initiation group to the surface of pigment particle.Triethoxysilyl group of Precursor 1 may be trimethoxysilyl group ortrichlorosilyl group.

The pigment particles may preferably have a function group, capable ofreacting with the precursor of the nitroxide-mediated polymerizationinitiation group, such as hydroxyl group. When the pigment particleshave no function group, the pigment particles may preferably beappropriately surface-treated to introduce the function group to asurface of pigment particles.

The reaction solvent is not particularly limited but it is possible touse dimethylsulfoxide, dimethylformamide, benzene, toluene, xylene, etc.

In the reaction formula (1-I) shown above, Precursor 1 of thenitroxide-mediated polymerization initiation group may be replaced withPrecursors 2 to 13 shown below, wherein n is an integer of 1 - 10 andtriethoxysilyl group may be replaced with trimethoxysilyl group ortrichlorosilyl group.

(Nitroxide-Mediated Polymerization)

Next, a step of forming a polymer chain by using, as the core particles,the particles to which the atom nitroxide-mediated polymerizationinitiation group is introduced through the reaction formula (1-I) willbe described.

After the core particles are dispersed in the reaction solvent, apolymerizable monomer for constituting the polymer chain is added andthen an atmosphere of the reaction system is replaced with inert gas toeffect the atom transfer radical polymerization.

The reaction solvent is not particularly limited so long as the pigmentparticles are dispersed in the reaction solvent. Examples of thereaction solvent may include dimethyl sulfoxide, dimethylformamide,benzene, toluene, xylene, diephenyl ether, etc. Alternatively, thepolymerization may be performed without using the reaction solvent.

As the inert gas, it is possible to use nitrogen or argon.

A polymerization temperature is in the range of 40-150° C., preferably60-120° C. Below 40° C., the polymer chain formed undesirably has a lowmolecular weight and the polymerization does not readily proceed.

During the polymerization, it is preferable that a free polymerizationinitiation group (species) which is not fixed at the particle surface isadded. As free polymer obtained from the free polymerization initiationgroup can be used as an index of a molecular weight and a molecularweight distribution of the polymer chain grafted to the particle.

As the free polymerization initiation group, it is preferable that thesame group as the nitroxide-mediated polymerization initiation groupfixed at the particle surface is selected. More specifically, withrespect to the particles obtained through the reaction formula (1-I),nitroxide similar to Precursor 1 is preferred.

After the reaction, the formed particles are separated and purified byan appropriate method, such as filtration, decantation, precipitationfractionation, centrifugation, or the like, and then are subjected todrying and classification to obtain electrophoretic particles.

The electrophotographic particles may preferably have a concentration of0.5-50 wt. %, more preferably 1-30 wt. %, per the weight of theelectrophoretic dispersion medium.

(Polymerizable Monomer Providing Polymer Chain and Polymer Chain)

It is possible to provide the polymer chain of the above describedelectrophoretic particles with an electric charge function and adispersion function.

First, the polymer chain having the dispersion function will bedescribed.

The polymer chain having the dispersion function is characterized inthat it is a polymer having a high affinity for the electrophoreticdispersion medium. The high affinity means that the polymer chain andthe electrophoretic dispersion medium are excellent in mutual solubilitywithout causing phase separation. The polymer chain has astearic-exclusion effect of preventing agglomeration between particlesby possessing an expanse in the electrophoretic dispersion medium.

As the polymerizable monomer providing the polymer chain having thedispersion function, as described above, the resultant polymer isrequired to have the high affinity with the electrophoretic dispersionmedium. Examples of the polymerizable monomer may include 1-hexene,1-heptene, 1-octene, 1-decene, butadiene, isoprene, isobutylene, etc.These may be used singly or in combination of two or more species.

Next, the polymer chain having the charge function will be described.

As the polymerizable monomer providing the polymer chain having thecharge function, it is possible to use a basic polymerizable monomer, anacidic polymerizable monomer, and a fluorine-containing polymerizablemonomer.

Examples of the basic polymerizable monomer may include: methyl(meth-)acrylate, ethyl (meth-)acrylate, propyl (meth-)acrylate, pentyl(meth-)acrylate, hexyl (meth-)acrylate, 2-ethylhexyl (meth-) acrylate,heptyl (meth-)acrylate, octyl (meth)-acrylate, nonyl (meth-)acrylate,decyl (meth-)acrylate, dodecyl (meth-)acrylate, tetradecyl(meth-)acrylate, hexadecyl (meth-)acrylate, octadecyl (meth-)acrylate,aminomethyl (meth-)acrylate, aminoethyl (meth-)acrylate,N,N-dimethylaminomethyl (meth-)acrylate, N,N-dimethylaminoethyl(meth-)acrylate, (meth-)acrylamide, N,N-dimethyl (meth-)acrylamide,N,N-diethyl (meth-)acrylamide, 4-vinylpyridine, etc.

When an acidic additive is added to the polymer chain obtained from thebasic polymerizable monomer, an acid-base interaction between thesesubstances are caused to occur, thus imparting positive chargeability tothe particles. Further, the polymer chain having the charge function canalso have the dispersion function by appropriately selecting the kindsof the basic polymerizable monomer and the acidic additive and byappropriately adjusting an addition amount of the acidic additive, sothat it is not necessary to effect grafting of the polymerizable monomerhaving the dispersion substance to the particle.

As the acidic additive, an acidic substance which is soluble in theelectrophoretic dispersion medium is preferred. For example, it ispossible to use rosin acid, rosin ester, rosin acid derivative,poly(meth-)acrylic acid, polyisobutylenesuccinic acid anhydride, etc.

An addition amount of the acidic additive may appropriately addeddepending on the kind thereof but may preferably be 0.001-10 wt. %,preferably 0.01-5 wt. %, with respect to the electrophoretic dispersionmedium.

On the other hand, examples of the acidic polymerizable monomer mayinclude: (meth-)acrylic acid. 2-butenoic acid (crotonic acid),3-butenoic acid (vinylacetic acid), 3-methyl-3-butenoic acid,3-pentenoic acid, 4-pentenoic acid, 4-methyl-4-pentenoic acid,4-hexenoic acid, 5-hexenoic acid, 5-methyl-5-hexenoic acid, 5-heptenoicacid, 6-heptenoic acid, 6-methyl-6-heptenoic acid, 6-octenoic acid,7-octenoic acid, 8-decenoic acid, 9-decenoic acid, 3-phenyl-2-propenoicacid (cinnamic acid), carboxymethyl (meth-)acrylate, carboxyethyl(meth-)acrylate, vinyl benzoic acid, vinylphenyl acetic acid,vinylphenyl propionic acid, maleic acid, fumaric acid, methylenesuccinicacid (itaconic acid), hydroxyl styrene, styrenesulfonic acid,vinyltoluenesulfonic acid, vinylsulfonic acid, sulfoethyl(meth-)acrylate, 2-sulfoethyl (meth-)acrylate, 2-propene-1-sulfonicacid, 2-methyl-2-propene-1-sulfonic acid, etc.

When a basic additive is added to the polymer chain obtained from theacidic polymerizable monomer, an acid-base interaction between thesesubstances are caused to occur, thus imparting negative chargeability tothe particles. Further, the polymer chain having the charge function canalso have the dispersion function by appropriately selecting the kindsof the acidic polymerizable monomer and the basic additive and byappropriately adjusting an addition amount of the basic additive, sothat it is not necessary to effect grafting of the polymerizable monomerhaving the dispersion substance to the particle.

As the basic additive, a basic substance which is soluble in theelectrophoretic dispersion medium is preferred. For example, it ispossible to use polyisobutylsucccinimide, polyvinyl pyridine, pyridine,lecithin, polyvinyl acetate, polyethylene oxide polymethyl methacrylate,polydecyl methacrylate, polydodecyl methacrylate, polyoctadecylmethacrylate, polyacrylamide, polyester, polyether, etc.

An addition amount of the basic additive may appropriately addeddepending on the kind thereof but may preferably be 0.001-10 wt. %,preferably 0.01-5 wt. %, with respect to the electrophoretic dispersionmedium.

Further, examples of the fluorine-containing polymerizable monomer mayinclude: (meth-)acrylate, 2,2,2-trifluoroethyl (meth-)acrylate,pentafluoroethyl (meth-)acrylate, heptafluoropropyl (meth-)acrylate,3,3,3-trifluoropropyl (meth-)acrylate, nonafluorobutyl (meth-)acrylate,3,3,4,4,4-pentafluorobutyl (meth-)acrylate, undecafluoropentyl(meth-)acrylate, 4,4,5,5,5-pentafluoropentyl (meth-)acrylate,tridecafluorohexyl (meth-)acrylate, pentadecafluoro-heptyl(meth-)acrylate, etc.

The polymer chain obtained from the fluorine-containing polymerizablemonomer has fluorine (atom) which has a large electronegativity, so thatit is possible to impart negative chargeability to the particle. Thepolymer chain has such an affinity with the electrophoretic dispersionmedium that it is not so high, thus being preferably one obtainedthrough block polymerization between the fluorine-containingpolymerizable monomer and the polymerizable monomer having thedispersion function.

The grafted polymer chain is characterized in that it has a molecularweight distribution index (weight-average molecularweight/number-average molecular weight) which is controlled to be notmore than 1.8, preferably not more than 1.5, further preferably not morethan 1.3. When the molecular weight distribution index of the graftedpolymer chain exceeds 1.8, it is difficult to say that the chain lengthof polymer chain is uniform and the electrophoretic particles areundesirably liable to cause unevenness in dispersibility andchargeability.

The number-average molecular weight may appropriately be determineddepending on whether the polymer chain is of the dispersionfunction-type or the charge function-type. In the case where the polymerchain is of the dispersion function-type, the number-average molecularweight may preferably be in the range of 500-1,000,000 more preferably1,000-500,000. Below 500, it is difficult for the polymer chain to havethe dispersion function. Above 1,000,000, the solubility in theelectrophoretic dispersion medium is undesirably lowered.

A graft density of the polymer chain can be controlled by a degree ofintroduction of the nitroxide-mediated polymerization initiation group.Further, the chain length of the polymer chain can be controlled by theaddition amount of the polymerizable monomer, the polymerization time,etc.

(Pigment)

As the pigment particles as the core particles constituting theelectrophoretic particles, it is possible to use an organic pigmentparticles, inorganic pigment particles, etc.

Examples of the organic pigment particles may include particles of: azopigments, phthalocyanine pigments, quinacridone pigments, isoindolinonepigments isoindolin pigments, dioxazine pigments, perylene pigments,perinone pigments, thioindigo pigments, quinophthalone pigments,anthraquinone pigments, nitro pigments, and nitroso pigments. Specificexamples thereof may include: red pigments, such as Quinacridone Red,Lake Red, Brilliant Carmine, Perylene Red, Permanent Red, Toluidine Redand Madder Lake; green pigments, such as Diamond Green Lake,Phthalocyanine Green, and Pigment Green; blue pigments, such as VictoriaBlue Lake, Phthalocyanine Blue, and Fast Sky Blue; yellow pigments, suchas Hansa Yellow, Fast Yellow, Disazo Yellow, Isoindolinone Yellow, anQuinophthalone Yellow; and black pigments, such as Aniline Block andDiamond Black.

Examples of the inorganic pigment particles may include particles of:white pigments, such as titanium oxide, aluminum oxide, zinc oxide, leadoxide, and zinc sulphide; black pigments, such as carbon black,magnetite, manganese ferrite black, cobalt ferrite black, and titaniumblack; red pigments, such as cadmium red, red iron oxide, and molybdenumred; green pigments, such as chromium oxide, viridian, titanium cobaltgreen, cobalt green, and victoria green; blue pigments, such asultramarine blue, prussian blue, and cobalt blue; and yellow pigments,such as cadmium yellow, titanium yellow, yellow iron oxide, chromeyellow, and antimony yellow.

The pigment may preferably have an average particle size of 10 nm to 2μm, more preferably 20 nm to 1 μm. Below 10 nm, a handlingcharacteristic is undesirably lowered considerably. Above 2 μm, a degreeof pigmentation ((color) definition) of the pigment is desirablylowered.

(Application to Electrophoretic Display Device)

Hereinbelow, an embodiment of an electrophoretic display device usingelectrophoretic particles of this (First) invention will be describedwith reference to the drawings.

FIGS. 1(a) and 1(b) are schematic sectional views each showing anembodiment of the electrophoretic display device using theelectrophotographic particles of the present invention.

As shown in FIG. 1(a), the electrophoretic display device includes afirst substrate 1 a provided with a first electrode 1 c a secondsubstrate 1 b provided with a second electrode 1 d which are disposedopposite to each other with a predetermined spacing through a partitionwall 1 g. In a cell (space) defined by the pair of first and secondsubstrates 1 a and 1 b and the partition wall 1 g, an electrophoreticdispersion liquid comprising at least electrophoretic particles 1 e andan electrophoretic dispersion medium if is sealed. On each of theelectrodes 1 c and 1 d, an insulating layer 1 h is formed. A displaysurface of the electrophoretic display device is located on the secondsubstrate 1 b side.

FIG. 1(b) shows an electrophoretic display device using microcapsules.On a first substrate 1 a, a plurality of microcapsules 1 i eachcontaining the electrophoretic dispersion liquid are disposed andcovered with a second substrate 1 b. In the case of using themicrocapsules 1 i, the insulating layer 1 h may be omitted.

In FIGS. 1(a) and 1(b), the first electrode 1 c comprises a plurality ofelectrode portions as pixel electrodes capable of independently applyinga desired electric field to the electrophoretic dispersion liquid ineach cell (or each microcapsule), and the second electrode 1 d is acommon electrode through which the same potential is applied to theentire display area.

The first electrode 1 c (pixel electrode) is provided with an unshownswitching element (for each electrode portion) and is supplied with aselection signal from an unshown matrix drive circuit row by row andalso supplied with a control signal and an output from an unshown drivetransistor column by column. As a result, it is possible to apply adesired electric field to the electrophoretic dispersion liquid(electrophoretic particles 1 e) in each of the cells groups.

The electrophoretic particles 1 e in each individual cell (ormicrocapsule) are controlled by an electric field applied through thefirst electrode 1 c, whereby at each pixel, the color (e.g., white) ofthe electrophoretic particles 1 e and the color (e.g., blue) of thedispersion medium 1 f are selectively displayed. By effecting such adrive on a pixel-by-pixel basis, it is possible to effect display ofarbitrary images and characters by use of corresponding pixels.

(Constitution of Electrophoretic Display Device)

The first substrate 1 a is formed of any insulating member, forsupplying the electrophoretic display device, such a glass, plastic, orthe like.

As the first electrode 1 c, it is possible to use a (vapor-)depositionfilm of ITO (indium tin oxide), tin oxide, indium oxide, gold, chromium,or the like. Pattern formation of the first electrode 1 c can beperformed by photolithography.

The second substrate 1 b may be a transparent substrate or a transparentplastic substrate.

As the second electrode 1 d, it is possible to use a transparentelectrode of a film of ITO or an organic conductive material.

The insulating layer 1 h can be formed of a colorless transparentinsulating resin, such as acrylic resin, epoxy resin, fluorine-basedresin, silicone resin, polyimide resin, polystyrene resin, or polyalkeneresin.

The partition wall 1 g can be formed of a polymeric material through anymethod including, e.g., a method wherein the partition wall is formedwith a photosensitive resin through the photolithographic process, amethod wherein the partition wall which has been prepared in advance isbonded to the substrate, a method wherein the partition wall is formedthrough molding, or the like.

The method of filling the electrophoretic dispersion liquid is notparticularly limited but can be an ink jet method using nozzles.

(Application to Microcapsule-Type Electrophoretic Display Device)

The microcapsule 1 i containing therein the electrophoretic dispersionliquid described above can be prepared through a known method, such asinterfacial polymerization, in situ polymerization, coacervation, or thelike.

As a material for the microcapsule 1 i, a high light-transmissivematerial may preferably be used. Examples thereof may include:urea-formaldehyde resin, melamine-formaldehyde resin, polyester,polyurethane, polyamide, polyethylene, polystyrene, polyvinyl alcohol,gelatine, their copolymers, and so on.

The method of forming the microcapsules 1 i on the first substrate 1 ais not particularly restricted but may be an ink jet method usingnozzles.

Incidentally, in order to prevent positional deviation of themicrocapsule 1 i disposed on the substrate, a light-transmissive resinbinder may be filled in a gap between adjacent microcapsules to fix themicrocapsules on the substrate. As the resin binder, it is possible touse polyvinyl alcohol, polyurethane, polyester, acrylic resin, siliconeresin, etc.

In the case of sealing a spacing between the first and second substrates1 a and 1 b, the spacing may preferably be sealed under pressure so thatthe microcapsule 1 i has such a shape that a horizontal length is longerthan a vertical length with respect to the first substrate 1 a (FIG.1(b)).

(Electrophoretic Dispersion Medium)

As the electrophoretic dispersion medium, it is possible to use aliquid, which is high insulative and colorless and transparent,including: aliphatic hydrocarbons, such as hexane, cyclohexane,kerosine, normal paraffin, isoparaffin, etc. These may be used singly orin mixture of two or more species.

The electrophoretic dispersion medium may be colored with oil solubledye having a color of R (red), G (green), B (blue), C (cyan), M(magenta), Y (yellow), etc. Examples of the dye may preferably includeazo dyes, anthraquinone dyes, quinoline dyes, nitro dyes, nitroso dyes,penoline dyes, phthalocyanine dyes, metal complex salt dyes, naphtholdyes, benzoquinone dyes, cyanine dyes, indigo dyes, quinoimine dyes,etc. These may be used in combination.

Examples of the oil soluble dye may include Vali Fast Yellow (1101,1105, 3108, 4120), Oil Yellow (105, 107, 129, 3G, GGS), Vali Fast Red(1306, 1355, 2303, 3304, 3306, 3320), Oil Pink 312, Oil Scarlet 308, OilViolet 730, Vali Fast Blue (1501, 1603, 1605. 1607 2606, 2610, 3405).Oil Blue (2N, BOS, 613), Macrolex Blue RR, Sumiplast Green G. Oil Green(502, BG), etc. A concentration of these dyes may preferably be 0.1-3.5wt. %, per the electrophoretic dispersion medium 1 f.

(Electrophoretic Dispersion Liquid)

The dispersion liquid at least contain the electrophoretic particles 1 eand the electrophoretic dispersion medium 1 f. In order to electricallycharge the electrophoretic particles 1 e, it is preferable that theabove described acidic additive or basic additive is added in thedispersion liquid.

Display Embodiment 1

A display embodiment of another electrophoretic display device using theelectrophoretic particles 1 e according to the present invention isshown in FIGS. 2(a) and 2(b).

FIGS. 2(a) and 2(b) illustrate a display example wherein, e.g., anelectrophoretic dispersion liquid comprising white electrophoreticparticles 1 e and a blue electrophoretic dispersion medium 1 f is filledin a cell. The electrophoretic particles 1 e is negatively charged inthis case.

When the electrophoretic particles 1 e are collected on the surface ofthe second electrode 1 d as shown in FIG. 2(a) by applying anegative-polarity voltage to the first electrode 1 c while keeping thevoltage of the second electrode 1 d at 0 V, the cell looks white,attributable to the distribution of the white electrophoretic particles1 e, when viewed from above. On the other hand, when the electrophoreticparticles 1 e are collected on the surface of the first electrode 1 c asshown in FIG. 2(b), by applying a positive-polarity voltage to the firstelectrode while keeping the voltage of the second electrode 1 d at 0 V,the cell looks blue when viewed from above.

Display Embodiment 2

Another display embodiment of the electrophoretic display device usingthe electrophoretic particles 1 e according to the present invention isshown in FIGS. 3(a) and 3(b).

FIGS. 3(a) and 3(b) illustrate a display example wherein, e.g., anelectrophoretic dispersion liquid comprising positively charged whiteelectrophoretic particles 1 ew, negatively charged black electrophoreticparticles 1 eb, and a colorless and transparent electrophoreticdispersion medium 1 f is filled in a cell.

When the black electrophoretic particles 1 eb are collected on thesurface of the second electrode 1 d and the white electrophoreticparticles 1 ew are collected on the surface of the first electrode 1 c,as shown in FIG. 3(a) by applying a negative-polarity voltage to thefirst electrode 1 c while keeping the voltage of the second electrode 1d at 0 V, the cell looks black, attributable to the distribution of theblack electrophoretic particles 1 eb, when viewed from above. On theother hand, when the white electrophoretic particles 1 ew are collectedon the surface of the first electrode 1 d and the black electrophoreticparticles 1 eb are collected on the surface of the first electrode 1 c,as shown in FIG. 3(b), by applying a positive-polarity voltage to thefirst electrode while keeping the voltage of the second electrode 1 d at0 V, the cell looks white, attributable to the distribution of the whiteelectrophoretic particles 1 ew, when viewed from above.

The applied voltage varies depending on a charge amount of theelectrophoretic particles and a distance between the electrodes but isrequired to be several volts to several ten volts, and the gradationdisplay can be controlled by the applied voltage and an applicationtime.

By performing such a drive on a pixel-by-pixel basis, it is possible todisplay an arbitrary image or character by use of a multiplicity ofpixels.

(Horizontal Movement-Type Electrophoretic Display Device)

Hereinbelow, an embodiment of a horizontal movement-type electrophoreticdisplay device using electrophoretic particles of the present inventionwill be described with reference to the drawings.

FIGS. 4(a) and 4(b) are schematic sectional views each showing theembodiment of the horizontal movement-type electrophoretic displaydevice using the electrophotographic particles of the present invention.

As shown in FIG. 4(a), the electrophoretic display device includes afirst substrate 4 a on which a first electrode 4 c and a secondelectrode 4 d are disposed. Between the electrodes 4 c and 4 d and onthe second electrode 4 d, an insulating layer 4 h and an insulatinglayer 4 i are formed, respectively. The insulating layer 4 h formedbetween the electrodes 4 c and 4 d may be colored or may be colorlessand transparent, but the insulating layer 4 i is colorless andtransparent.

The electrophoretic display device further includes a second substrate 4b disposed opposite to the first substrate 4 a with a predeterminedspacing through a partition wall 4 g. In a cell (space) defined by thepair of first and second substrates 4 a and 4 b and the partition wall 4g, an electrophoretic dispersion liquid comprising at leastelectrophoretic particles 4 e and an electrophoretic dispersion medium 4f is sealed. A display surface of the electrophoretic display device islocated on the second substrate 4 b side.

FIG. 4(b) shows an electrophoretic display device using microcapsules.On a first substrate 4 a, a plurality of microcapsules 4 i eachcontaining the electrophoretic dispersion liquid are disposed andcovered with a second substrate 4 b. In the case of using themicrocapsules 4 i, the insulating layer 4 i may be omitted.

In FIGS. 4(a) and 4(b), the second electrode 4 d comprises a pluralityof electrode portions as pixel electrodes capable of independentlyapplying a desired electric field to the electrophoretic dispersionliquid in each cell (or each microcapsule), and the first electrode 4 cis a common electrode through which the same potential is applied to theentire display area.

The second electrode 4 d (pixel electrode) is provided with an unshownswitching element (for each electrode portion) and is supplied with aselection signal from an unshown matrix drive circuit row by row andalso supplied with a control signal and an output from an unshown drivetransistor column by column. As a result, it is possible to apply adesired electric field to the electrophoretic dispersion liquid(electrophoretic particles 4 e) in each of the cells groups.

The electrophoretic particles 4 e in each individual cell (ormicrocapsule) are controlled by an electric field applied through thesecond electrode 4 d whereby at each pixel, the color (e.g., black) ofthe electrophoretic particles 4 e and the color (e.g., white) of theinsulating layer 4 h are selectively displayed. By effecting such adrive on a pixel-by-pixel basis, it is possible to effect display ofarbitrary images and characters by use of corresponding pixels.

(Constitution of Electrophoretic Display Device)

The first substrate 4 a is formed of any insulating member, forsupplying the electrophoretic display device, such a glass, plastic, orthe like.

The second substrate 4 b may be a transparent substrate or a transparentplastic substrate.

The first electrode 4 c is a metal electrode of, e.g., Al exhibitinglight reflection performance.

The insulating layer 4 h formed on the first electrode 4 c is formed ofa mixture of a transparent colorless insulating resin with lightscattering fine particles of, e.g., aluminum oxide or titanium oxide. Asa material for the transparent colorless insulating resin, it ispossible use the above described insulating resins. Alternatively, it isalso possible to use a light scattering method utilizing unevenness atthe surface of the metal electrode without using the fine particles.

The second electrode 4 d is formed of an electroconductive material,which looks dark black from the viewer side of the electrophoreticdisplay device, such as titanium carbide, black-treated Cr, and Al or Tiprovided with a black surface layer. Pattern formation of the secondelectrode 5 may be performed through a photolithographic process.

On the second electrode 4 d, the insulating layer 4 i is formed of,e.g., the transparent colorless insulating resin described above.

In this embodiment, a display contrast is largely depend on an arealratio between the second electrode 4 d (each electrode portion) and anassociated pixel, so that an exposed area of the second electrode 4 d isrequired to be smaller than that of the pixel in order to enhance acontrast. For this reason, it is preferable that the areal ratiotherebetween may ordinarily be 1:2 to 1:5.

The partition wall 4 g may be formed in the same manner as describedabove. The method of filling the above described electrophoreticdispersion liquid in the cell is not limited particularly but may be theabove described ink jet method using nozzles.

(Application to Microcapsule-Type Electrophoretic Display Device)

The microcapsule 4 j containing the electrophoretic dispersion liquidcan be prepared by the known method as described above, such asinterfacial polymerization in situ polymerization, coacervation, and soon. The material for forming the microcapsule 3 j may be the samepolymer as described above.

The method of forming the microcapsules 4 j on the first substrate 4 ais not particularly restricted but may be the above described ink jetmethod using nozzles.

Incidentally, in order to prevent positional deviation of themicrocapsule 4 i disposed on the substrate, a light-transmissive resinbinder may be filled in a gap between adjacent microcapsules to fix themicrocapsules on the substrate. As the resin binder, it is possible touse the above described resin.

In the case of sealing a spacing between the first and second substrates4 a and 4 b, the spacing may preferably be sealed under pressure so thatthe microcapsule 4 i has such a shape that a horizontal length is longerthan a vertical length with respect to the first substrate 1 a (FIG.4(b)).

(Electrophoretic Dispersion Medium)

As the electrophoretic dispersion medium 4 f, it is possible to use theabove described liquids.

(Electrophoretic Particles)

As the electrophoretic particles 4 e, it is possible to use blackparticles (obtained by the same method as that described above). In thisembodiment, a concentration of the electrophotographic particles 4 e maypreferably 0.5-10 wt. %, more preferably 1-5 wt. %, per the weight ofthe electrophoretic dispersion medium 4 f although it varies dependingon the particle size of the electrophoretic particles 4 f. When theconcentration of the electrophotographic particles 4 e is less than 0.5wt. %, the first electrode 4 c cannot be covered completely, so that adisplay contrast is undesirably lowered. Further, when the concentrationof the electrophotographic particles 4 e exceeds 10 wt. %, theelectrophotographic particles extend off the colored second electrode 4d, thus undesirably lowering the display contrast.

Display Embodiment

A display embodiment of the horizontal movement-type electrophoreticdisplay device using the electrophoretic particles according to thisembodiment is shown in FIGS. 5(a) and 5(b).

FIGS. 5(a) and 5(b) illustrate a display example wherein, e.g., anelectrophoretic dispersion liquid comprising black electrophoreticparticles 3 e and a colorless and transparent electrophoretic dispersionmedium 4 f is filled in a cell. The electrophoretic particles 4 e isnegatively charged in this case.

In the case where the color of the surface of the insulating layer 4 his white and the color of the surface of the second electrode 4 d isblack, when the electrophoretic particles 4 e are collected on thesurface of the second electrode 4 d as shown in FIG. 5(a) by applying apositive-polarity voltage to the second electrode while keeping thevoltage of the first electrode 4 c at 0 V, the cell looks white whenviewed from above.

The applied voltage varies depending on a charge amount of theelectrophoretic particles and a distance between the electrodes but isrequired to be several volts to several ten volts, and the gradationdisplay can be controlled by the applied voltage and an applicationtime.

By performing such a drive on a pixel-by-pixel basis, it is possible todisplay an arbitrary image or character by use of a multiplicity ofpixels.

(2) Embodiments According to Second Invention

In an embodiment according to the second aspect of the present inventionelectrophoretic particles are particles provided with a polymer chainconnected to a surface of pigment particle, and the polymer chaincomprises a polymer, having a high affinity for a hydrocarbon dispersionmedium, obtained through living radical polymerization from the livingradical polymerization initiation group located at the pigment particlesurface. As a result, it is possible to obtain electrophoretic particleshaving a high dispersion function while preventing agglomeration ofparticles in the dispersion medium.

Further, by connecting a polymer chain having a high (electrical) chargefunction, it is possible to enhance the charge function of the resultantelectrophoretic particles. It is also possible to form a polymer chaincomprising a copolymer, particularly a block copolymer, consisting ofthe polymer chain having the charge function and the polymer chainhaving the dispersion function.

The electrophoretic particles are obtained by introducing the livingradical polymerization initiation group to the pigment particle surfaceand grafting the polymer chain from the living radical polymerizationinitiation group by living radical polymerization.

The living radical polymerization may be classified into atom transferradical polymerization, bb polymerization nitroxide-mediated, etc. Theliving radical polymerization may be any type thereof since the polymerchain having an affinity for the dispersion medium can be obtained byappropriately selecting monomers described later. The nitroxide-mediatedpolymerization may also preferably used in this (Second) invention sinceno catalyst is employed and thus the resultant electrophoretic particlesare less liable to cause a color change.

In this invention, the living radical polymerization is used, so that itis possible to arbitrarily design the kinds of monomers, a degree ofpolymerization, formation of copolymer, etc. As a result, it is possibleto finely control the chargeability and dispersibility of the polymerchain.

The electrophoretic particles in this invention can be utilized in theelectrophoretic display device or in the field of electrophotographyusing liquid toner.

(Introduction of Polymerization Initiation Group)

With respect to the cases where the living radical polymerization is theatom transfer radical polymerization and is the nitroxide-mediatedpolymerization, an introduction method of the polymerization initiationgroup will be described.

In the case where the living radical polymerization is thenitroxide-mediated polymerization, in accordance with a reaction formula(2-I) shown below, it is possible to introduce the nitroxide-mediatedpolymerization initiation group to the surface of pigment particle. Morespecifically, in a reaction solvent, the pigment particles and Precursor1 (shown below) of the nitroxide-mediated polymerization initiationgroup are added and reacted with each other to introduce thenitroxide-mediated polymerization initiation group to the surface ofpigment particle. Triethoxysilyl group of Precursor 1 may betrimethoxysilyl group or trichlorosilyl group.

The pigment particles may preferably have a function group, capable ofreacting with the precursor of the nitroxide-mediated polymerizationinitiation group, such as hydroxyl group. When the pigment particleshave no function group, the pigment particles may preferably beappropriately surface-treated to introduce the function group to asurface of pigment particles.

The reaction solvent is not particularly limited but it is possible touse dimethylsulfoxide, dimethylformamide, benzene, toluene, xylene, etc.

In the reaction formula (2-I) shown above, Precursor 1 of thenitroxide-mediated polymerization initiation group may be replaced withPrecursors 2 to 13 shown in the embodiment of First invention. Thetriethoxysilyl group in the precursors may be replaced withtrimethoxysilyl group or trichlorosilyl group.

In the case where the living radical polymerization is the atom transferradical polymerization, in accordance with a reaction formula (2-II)shown below, it is possible to introduce the atom transfer radicalpolymerization initiation group to the surface of pigment particle. Morespecifically, in a reaction solvent, the pigment particles and Precursor14 (shown below) of the atom transfer radical polymerization initiationgroup are added and reacted with each other to introduce the atomtransfer radical polymerization initiation group to the surface ofpigment particle. Trichlorosilyl group of Precursor 1 may betrimethoxysilyl group or triethoxysilyl group.

The pigment particles may preferably have a function group, capable ofreacting with the precursor of the atom transfer radical polymerizationinitiation group, such as hydroxyl group. When the pigment particleshave no function group, the pigment particles may preferably beappropriately surface-treated to introduce the function group to asurface of pigment particles.

The reaction solvent is not particularly limited but it is possible touse dimethylsulfoxide, dimethylformamide, benzene, toluene, xylene, etc.

In the reaction formula (2-II) shown above, Precursor 1 of the atomtransfer radical polymerization initiation group may be replaced withPrecursors 15 to 17 shown below, wherein n is an integer of 1-10 andtrichlorosilyl group may be replaced with trimethoxysilyl group ortriethoxysilyl group.

(Living Radical Polymerization)

With respect to the case where the living radical polymerization is thenitroxide-mediated polymerization, grafting of the polymer chain will bedescribed. It is possible to easily form polymer chains having a uniformchain length at the surfaces of core particles by using, as the coreparticles, the pigment particles provided with the introducednitroxide-mediated polymerization initiation group through the reactionformula (2-I).

After the core particles are dispersed in the reaction solvent, apolymerizable monomer for constituting the polymer chain is added andthen an atmosphere of the reaction system is replaced with inert gas toeffect the atom transfer radical polymerization.

The reaction solvent is not particularly limited so long as the pigmentparticles are dispersed in the reaction solvent. Examples of thereaction solvent may include dimethyl sulfoxide, dimethylformamide,benzene, toluene, xylene, diephenyl ether, etc. Alternatively, thepolymerization may be performed without using the reaction solvent.

As the inert gas, it is possible to use nitrogen or argon.

A polymerization temperature is in the range of 40-150° C., preferably60-120° C. Below 40° C., the polymer chain formed undesirably has a lowmolecular weight and the polymerization does not readily proceed.

During the polymerization, it is preferable that a free polymerizationinitiation group (species) which is not fixed at the particle surface isadded. As free polymer obtained from the free polymerization initiationgroup can be used as an index of a molecular weight and a molecularweight distribution of the polymer chain grafted to the particle.

As the free polymerization initiation group, it is preferable that thesame group as the nitroxide-mediated polymerization initiation groupfixed at the particle surface is selected. More specifically, withrespect to the particles obtained through the reaction formula (1-I),nitroxide similar to Precursor 1 is preferred.

After the reaction, the formed particles are separated and purified byan appropriate method, such as filtration, decantation, precipitationfractionation, centrifugation, or the like, and then are subjected todrying and classification to obtain electrophoretic particles.

(Atom Transfer Radical Polymerization)

Next, the case where the living radical polymerization is the atomtransfer radical polymerization will be described.

By using, as the core particles, the pigment particles to which the atomtransfer radical polymerization initiation group is introduced throughthe reaction formula (2-II), it is possible to easily form polymerchains having a uniform chain length at the surfaces of core particles.

After the core particles are dispersed in the reaction solvent, apolymerizable monomer for constituting the polymer chain and a transfermetal complex are added and then an atmosphere of the reaction system isreplaced with inert gas to effect the atom transfer radicalpolymerization.

The reaction solvent is not particularly limited so long as the coreparticles are dispersed in the reaction solvent. Examples of thereaction solvent may include dimethyl sulfoxide, dimethylformamide,acetonitrile, pyridine, methanol, ethanol, propanol, butanol, pentanol,hexanol, heptanol, cyclohexanol, methyl cellosolve, ethyl cellosolve,isopropyl cellosolve, butyl cellosolve, acetone, methyl ethyl ketone,methyl isobutyl ketone, cyclohexanone, ethyl acetate, butyl acetate,ethyl propionate, dimethyl ether, diethyl ether, trioxane,tetrahydrofuran, pentane, cyclopentane, hexane, cyclohexane, heptane,octane, nonane, decane, benzene, toluene, xylene, ethylbenzene,methoxybenzene, etc. These may be used singly or in combination of twoor more species.

As the inert gas, it is possible to use nitrogen or argon.

The transfer metal complex used comprises halogenated metal and aligand. As a metal species of the halogenated metal, transfer metal fromTi (atomic member: 22) to Zn (atomic number: 30) are preferred. Ofthese, Fe, Co, Ni and Cu are further preferred. As the halogenatedmetal, cuprous chloride and cuprous bromide are particularly preferred.

The ligand is not particularly limited so long as it is capable ofcoordinating with the halogenated metal. Example thereof may include:2,2′-bipyridyl, 4,4′-di-(n-heptyl)-2,2′-bipyridyl,2-(N-pentyliminomethyl) pyridine, (-)-sparteine,tris(2-dimethylaminoethyl)amine, ethylenediamine, dimethylglyoxime,1,4,8,11-tetramethyl-1,4,8,11-tetraazocyclotetradecane,1,10-phenanthroline, N,N,N′,N″,N″-pentamethyldiethyltriamine,hexamethyl(2-aminoethyl)amine, etc.

The metal transfer complex may preferably be added in an amount of0.001-10 wt. %, more preferably 0.05-5 wt. %, with respect to thepolymerizable monomer constituting the polymer chain.

A polymerization temperature is in the range of 40-100° C., preferably50-80° C. Above 100° C., the polymer fine particles are undesirablymelted. Below 40° C., the polymer chain formed undesirably has a lowmolecular weight and the polymerization does not readily proceed.

During the polymerization, it is preferable that a free polymerizationinitiation group (species) which is not fixed at the particle surface isadded. As free polymer obtained from the free polymerization initiationgroup can be used as an index of a molecular weight and a molecularweight distribution of the polymer chain grafted to the particle.

As the free polymerization initiation group, it is preferable that thesame group as the atom transfer radical polymerization initiation groupfixed at the particle surface is selected. More specifically, withrespect to the particles obtained through the reaction formula (1-II),2-bromo ethyl isobutyrate is preferred. With respect to the particlesprovided with a fixed Precursor 15 at a surface of each particle,2-bromo ethyl propionate is preferred.

After the reaction, the formed particles are separated and purified byan appropriate method, such as filtration, decantation, precipitationfractionation, centrifugation, or the like, and then are subjected todrying and classification to obtain electrophoretic particles.

(Dispersion Function and Charge Function of Polymer Chain)

The electrophoretic particles in this invention have an electric chargefunction and a dispersion function.

First, the polymer chain having the dispersion function will bedescribed.

The polymer chain having the dispersion function is characterized inthat it is a polymer having a high affinity for the electrophoreticdispersion medium. The high affinity means that the polymer chain andthe electrophoretic dispersion medium are excellent in mutual solubilitywithout causing phase separation. The polymer chain has astearic-exclusion effect of preventing agglomeration between particlesby possessing an expanse in the electrophoretic dispersion medium.

As the polymerizable monomer providing the polymer chain having thedispersion function, as described above, the resultant polymer isrequired to have the high affinity with the electrophoretic dispersionmedium. Examples of the polymerizable monomer may include 1-hexene,1-heptene, 1-octene, 1-decene, butadiene, isoprene, isobutylene, etc.These may be used singly or in combination of two or more species.

Next, the polymer chain having the charge function will be described.

As the polymerizable monomer providing the polymer chain having thecharge function, it is possible to use a basic polymerizable monomer, anacidic polymerizable monomer, and a fluorine-containing polymerizablemonomer.

Examples of the basic polymerizable monomer may include those, such asmethyl (meth-)acrylate, as described in the embodiments of Firstinvention.

When an acidic additive is added to the polymer chain obtained from thebasic polymerizable monomer, an acid-base interaction between thesesubstances are caused to occur, thus imparting positive chargeability tothe particles. Further, the polymer chain having the charge function canalso have the dispersion function by appropriately selecting the kindsof the basic polymerizable monomer and the acidic additive and byappropriately adjusting an addition amount of the acidic additive, sothat it is not necessary to effect grafting of the polymerizable monomerhaving the dispersion substance to the particle.

As the acidic additive, an acidic substance which is soluble in theelectrophoretic dispersion medium is preferred. For example, it ispossible to use rosin acid, rosin ester, rosin acid derivative,poly(meth-)acrylic acid, polyisobutylenesuccinic acid anhydride, etc.

An addition amount of the acidic additive may appropriately addeddepending on the kind thereof but may preferably be 0.001-10 wt. %,preferably 0.01-5 wt. %, with respect to the electrophoretic dispersionmedium.

On the other hand, examples of the acidic polymerizable monomer mayinclude those, such as (meth-)acrylic acid, as described in theembodiments of First invention.

When a basic additive is added to the polymer chain obtained from theacidic polymerizable monomer, an acid-base interaction between thesesubstances are caused to occur, thus imparting negative chargeability tothe particles. Further, the polymer chain having the charge function canalso have the dispersion function by appropriately selecting the kindsof the acidic polymerizable monomer and the basic additive and byappropriately adjusting an addition amount of the basic additive, sothat it is not necessary to effect grafting of the polymerizable monomerhaving the dispersion substance to the particle.

As the basic additive, a basic substance which is soluble in theelectrophoretic dispersion medium is preferred. For example, it ispossible to use those, such as polyisobutylsucccinimide, as described inthe embodiments of First invention.

An addition amount of the basic additive may appropriately addeddepending on the kind thereof but may preferably be 0.001-10 wt. %,preferably 0.01 5 wt. %, with respect to the electrophoretic dispersionmedium.

Further, examples of the fluorine-containing polymerizable monomer mayinclude those, such as (meth-)acrylate, as described in the embodimentsof First invention.

The polymer chain obtained from the fluorine-containing polymerizablemonomer has fluorine (atom) which has a large electronegativity, so thatit is possible to impart negative chargeability to the particle. Thepolymer chain has such an affinity with the electrophoretic dispersionmedium that it is not so high, thus being preferably one obtainedthrough block polymerization between the fluorine-containingpolymerizable monomer and the polymerizable monomer having thedispersion function.

The grafted polymer chain is characterized in that it has a molecularweight distribution index (weight-average molecularweight/number-average molecular weight) which is controlled to be notmore than 1.8, preferably not more than 1.5, further preferably not morethan 1.3. When the molecular weight distribution index of the graftedpolymer chain is in the range, the chain length of polymer chain becomesuniform, so that it is possible to suppress unevenness in dispersibilityand chargeability of the electrophoretic particles.

The number-average molecular weight may appropriately be determineddepending on whether the polymer chain is of the dispersionfunction-type or the charge function-type. In the case where the polymerchain is of the dispersion function-type, the number-average molecularweight may preferably be in the range of 500-1,000,000 more preferably1,000-500,000. By forming the polymer chain having the molecular weightin this range, the dispersion function can be readily performed and thesolubility in the electrophoretic dispersion medium can be kept.

A graft density of the polymer chain can be controlled by a degree ofintroduction of living radical polymerization initiation group or thenitroxide-mediated polymerization initiation group. Further, the chainlength of the polymer chain can be controlled by the addition amount ofthe polymerizable monomer, the polymerization time, etc.

(Pigment)

As the pigment particles constituting the electrophoretic particles, itis possible to use an organic pigment particles, inorganic pigmentparticles, etc.

Examples of the organic pigment particles may include those, such as azopigments particles, as described in the embodiments of First invention.

Examples of the inorganic pigment particles may include those, such aswhite pigments particles, as described in the embodiments of Firstinvention.

The pigment may preferably have an average particle size of 10-500 nm,more preferably 20-200 nm. Below 10 nm, a handling characteristic isundesirably lowered considerably. Above 500 nm, a degree of pigmentation((color) definition) of the pigment is desirably lowered.

(Application to Electrophoretic Display Device)

Similarly as in the embodiments of the electrophoretic display devicesdescribed in the First invention with reference to the FIGS. 1 to 5, theelectrophoretic particles in this (Second) invention are also applicableto the electrophoretic display devices described in First invention.

Hereinbelow, First invention will be described more specifically basedon Examples but is not limited thereto.

EXAMPLE 1-1

In toluene, titanium oxide particles (average particle size: 200 nm,having hydroxy group at particle surface) and Precursor 1 (n=10) ofnitroxide-mediated polymerization initiation group are reacted with eachother to introduce nitroxide-mediated polymerization initiation group atthe particle surface of titanium oxide particles. After the titaniumoxide particles are dispersed in toluene, in the resultant system,dodecyl acrylate is added. The reaction system is aerated with nitrogenand subjected to nitroxide-mediated polymerization at 90° C. for apredetermined time. In this case, nitroxide similar to Precursor 1 ofthe nitroxide-mediated polymerization initiation group as a freepolymerization initiation group (radical) is added in the reactionsystem in advance so as to provide an index of molecular weight andmolecular weight distribution of a polymer chain grafted to the particlesurface of titanium oxide particles.

After the polymerization, the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles.

The electrophoretic particles are well dispersed in chloroform, so thatit is possible to confirm that dodecyl polyacrylate is grafted at theparticle surface of titanium oxide. Further, when a polymer obtainedfrom Nitroxide 1 added as the free polymerization initiation group issubjected to measurement of molecular weight and molecular weightdistribution, the polymer has a number-average molecular weight of about50,000 and a molecular weight dispersion index (weight-average molecularweight/number-average molecular weight) of 1.20. As a result, it ispossible to confirm that the polymer chains grafted to the coreparticles have a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 5 wt. % of theelectrophoretic particles (white particles), 0.1 wt. % of a colorant(“Oil Blue N”, mfd. by Aldrich Co.), 2.5 wt. % of rosin acid (acidicadditive), and 92.9 wt. % of an electrophoretic dispersion medium(“Isoper H”, mfd. by Exxon Corp.). The electrophoretic particles arepositively charged by acid-base interaction between the grafted dodecylpolyacrylate and rosin acid. Further, the grafted dodecyl polyacrylatehas an expanse in the electrophoretic dispersion medium, thus havingalso a dispersion function.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 1(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearblue/white display.

EXAMPLE 1-2

A plurality of microcapsules 1 i each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 1-1 areprepared by in-situ polymerization method. Each microcapsule is formedof urea-formaldehyde resin as a film-forming material. Anelectrophoretic display device, as shown in FIG. 1(b), which isconnected with a voltage application circuit is prepared by disposingthe plurality of microcapsules 1 i on a first substrate 1 a by use ofnozzles according to the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles are excellent in dispersibility,chargeability, and (color) definition and it is possible to effect clearblue/white display.

EXAMPLE 1-3

In toluene, magnetite particles (average particle size: 200 nm, havinghydroxy group at particle surface) and Precursor 1 (n=10) ofnitroxide-mediated polymerization initiation group are reacted with eachother to introduce nitroxide-mediated polymerization initiation group atthe particle surface of magnetite particles. After the magnetiteparticles are dispersed in toluene, in the resultant system, dodecylacrylate is added. The reaction system is aerated with nitrogen andsubjected to nitroxide-mediated polymerization at 90° C. for apredetermined time. In this case, nitroxide similar to Precursor 1 ofthe nitroxide-mediated polymerization initiation group as a freepolymerization initiation group (radical) is added in the reactionsystem in advance so as to provide an index of molecular weight andmolecular weight distribution of a polymer chain grafted to the particlesurface of magnetite particles.

After the polymerization, the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles 4 e.

The electrophoretic particles 4 e are well dispersed in chloroform, sothat it is possible to confirm that octadecyl polyacrylate is grafted atthe particle surface of magnetite. Further, when a polymer obtained fromthe nitroxide added as the free polymerization initiation group issubjected to measurement of molecular weight and molecular weightdistribution, the polymer has a number-average molecular weight of about80,000 and a molecular weight dispersion index (weight-average molecularweight/number-average molecular weight) of 1.26. As a result, it ispossible to confirm that the polymer chains grafted to the magnetiteparticles have a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 1 wt. % of theelectrophoretic particles 4 e (black particles), 0.5 wt. % of rosin acid(acidic additive), and 98.5 wt. % of an electrophoretic dispersionmedium 4 f (“Isoper H”, mfd. by Exxon Corp.). The electrophoreticparticles 4 e are positively charged by acid-base interaction betweenthe grafted octadecyl polyacrylate and rosin acid. Further, the graftedoctadecyl polyacrylate has an expanse in the electrophoretic dispersionmedium 4 f, thus having also a dispersion function.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 4(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 1-4

A plurality of microcapsules 4 j each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 1-3 areprepared by interfacial polymerization method. Each microcapsule isformed of polyamide resin as a film-forming material. An electrophoreticdisplay device, as shown in FIG. 4(b), which is connected with a voltageapplication circuit is prepared by disposing the plurality ofmicrocapsules 4 j on a first substrate 4 a by use of nozzles accordingto the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,and chargeability, and it is possible to effect clear white/blackdisplay.

EXAMPLE 1-5

In toluene, magnetite particles (average particle size: 200 nm, havinghydroxy group at particle surface) and Precursor 5 (n=10) ofnitroxide-mediated polymerization initiation group are reacted with eachother to introduce nitroxide-mediated polymerization initiation group atthe particle surface of magnetite particles. After the magnetiteparticles are dispersed in dimethylformamide, in the resultant system,acrylic acid is added. The reaction system is aerated with nitrogen andsubjected to nitroxide-mediated polymerization at 100° C. for apredetermined time. After acrylic acid is consumed, isoprene is added tothe reaction system in a molar ratio of (acrylic acid):(isoprene)=1:9 toform a graft polymer chain of block copolymer. In this case, nitroxidesimilar to Precursor 5 of the nitroxide-mediated polymerizationinitiation group as a free polymerization initiation group (radical) isadded in the reaction system in advance so as to provide an index ofmolecular weight and molecular weight distribution of a polymer chaingrafted to the particle surface of magnetite particles.

After the polymerization the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles 4 e.

The electrophoretic particles 4 e are well dispersed in chloroform, sothat it is possible to confirm that block copolymer of polyacrylic acidand polyisoprene is grafted at the particle surface of magnetite.Further, when a polymer obtained from the nitroxide added as the freepolymerization initiation group is subjected to measurement of molecularweight and molecular weight distribution, the polymer has anumber-average molecular weight of about 70,000 and a molecular weightdispersion index (weight-average molecular weight/number-averagemolecular weight) of 1.28. As a result, it is possible to confirm thatthe polymer chains grafted to the magnetite particles are the blockcopolymer having a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 1 wt. % of theelectrophoretic particles 4 e (black particles), 0.5 wt. % ofpolyisobutylenesuccinimide (basic additive), and 98.5 wt. % of anelectrophoretic dispersion medium 4 f (“Isoper H”, mfd.. by ExxonCorp.). The electrophoretic particles 4 e are positively charged byacid-base interaction between the grafted polyacrylic acid site of theblock copolymer and polyisobutylenesuccinimide. Further, the graftedpolyisoprene site of the block copolymer has an expanse in theelectrophoretic dispersion medium 4 f, thus having a dispersionfunction.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 4(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 1-6

A plurality of microcapsules 4 j each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 1-5 areprepared by interfacial polymerization method. Each microcapsule isformed of polyamide resin as a film-forming material. An electrophoreticdisplay device, as shown in FIG. 4(b), which is connected with a voltageapplication circuit is prepared by disposing the plurality ofmicrocapsules 4 j on a first substrate 4 a by use of nozzles accordingto the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 1-7

A nitroxide-mediated polymerization initiation group is introduced toeach particle surface of magnetite particles in the same manner as inExample 1-5. After the magnetite particles are dispersed indimethylformamide, in the resultant system, aminoethyl acrylate isadded. The reaction system is aerated with nitrogen and subjected tonitroxide-mediated polymerization at 100° C. for a predetermined time.After aminoethyl acrylate is consumed, isoprene is added to the reactionsystem in a molar ratio of (aminoethyl acrylate):(isoprene)=1:9 to forma graft polymer chain of block copolymer. In this case, nitroxidesimilar to Precursor 5 of the nitroxide-mediated polymerizationinitiation group as a free polymerization initiation group (radical) isadded in the reaction system in advance so as to provide an index ofmolecular weight and molecular weight distribution of a polymer chaingrafted to the particle surface of magnetite particles.

After the polymerization, the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles 4 e.

The electrophoretic particles 4 e are well dispersed in chloroform, sothat it is possible to confirm that block copolymer of polyacrylic acidand polyisoprene is grafted at the particle surface of magnetite.Further, when a polymer obtained from the nitroxide added as the freepolymerization initiation group is subjected to measurement of molecularweight and molecular weight distribution, the polymer has anumber-average molecular weight of about 60,000 and a molecular weightdispersion index (weight-average molecular weight/number-averagemolecular weight) of 1.29. As a result, it is possible to confirm thatthe polymer chains grafted to the magnetite particles are the blockcopolymer having a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 1 wt. % of theelectrophoretic particles 4 e (black particles), 0.5 wt. % of rosin acid(acidic additive), and 98.5 wt. % of an electrophoretic dispersionmedium 4 f (“Isoper H”, mfd. by Exxon Corp.). The electrophoreticparticles 4 e are positively charged by acid-base interaction betweenthe grafted polyaminoethyl acrylate site of the block copolymer andpolyisobutylenesuccinimide. Further, the grafted polyisoprene site ofthe block copolymer has an expanse in the electrophoretic dispersionmedium 4 f, thus having a dispersion function.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 4(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 1-8

A plurality of microcapsules 4 j each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 1-7 areprepared by in-situ polymerization method. Each microcapsule is formedof melamine-formaldehyde resin as a film-forming material. Anelectrophoretic display device, as shown in FIG. 4(b), which isconnected with a voltage application circuit is prepared by disposingthe plurality of microcapsules 4 j on a first substrate 4 a by use ofnozzles according to the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,changeability and (color) definition and it is possible to effect clearwhite/black display.

EXAMPLE 1-9

An electrophoretic dispersion liquid is prepared by using 5 wt. % ofelectrophoretic particles (white particles) obtained in the same manneras in Example 1-1, 2.5 wt. % of rosin acid (acidic additive), 3 wt. % ofelectrophoretic particles (black particles) obtained in the same manneras in Example 1-5, 1.5 wt. % of polyisobutylenesuccinimide (basicadditive), and 88 wt. % of an EDM (Isoper H). In the electrophoreticdispersion liquid, the white electrophoretic particles are positivelycharged and the black electrophoretic particles are negatively charged.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 1(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display (FIG. 3) for a long time by driving it at a drivevoltage of ±10 V, the electrophoretic particles are excellent indispersibility, chargeability and (color) definition, and it is possibleto effect clear white/black display.

EXAMPLE 1-10

A plurality of microcapsules 1 i each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 1-9 areprepared by in-situ polymerization method. Each microcapsule is formedof melamine-formaldehyde resin as a film-forming material. Anelectrophoretic display device, as shown in FIG. 1(b), which isconnected with a voltage application circuit is prepared by disposingthe plurality of microcapsules 1 i on a first substrate 1 a by use ofnozzles according to the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display (FIG. 3) for a long time by driving it at a drivevoltage of ±10 V, the electrophoretic particles are excellent indispersibility, chargeability and (color) definition, and it is possibleto effect clear white/black display.

Hereinbelow, Second invention will be described more specifically basedon Examples but is not limited thereto.

EXAMPLE 2-1

In toluene, titanium oxide particles (average particle size: 200 nm,having hydroxy group at particle surface) and Precursor 1 (n=10) ofnitroxide-mediated polymerization initiation group are reacted with eachother to introduce nitroxide-mediated polymerization initiation group atthe particle surface of titanium oxide particles. After the titaniumoxide particles are dispersed in toluene, in the resultant system,dodecyl acrylate is added. The reaction system is aerated with nitrogenand subjected to nitroxide-mediated polymerization at 90° C. for apredetermined time. In this case, nitroxide similar to Precursor 1 ofthe nitroxide-mediated polymerization initiation group as a freepolymerization initiation group (radical) is added in the reactionsystem in advance so as to provide an index of molecular weight andmolecular weight distribution of a polymer chain grafted to the particlesurface of titanium oxide particles.

After the polymerization, the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles.

The electrophoretic particles are well dispersed in chloroform, so thatit is possible to confirm that dodecyl polyacrylate is grafted at theparticle surface of titanium oxide. Further, when a polymer obtainedfrom Nitroxide 1 added as the free polymerization initiation group issubjected to measurement of molecular weight and molecular weightdistribution, the polymer has a number-average molecular weight of about50,000 and a molecular weight dispersion index (weight-average molecularweight/number-average molecular weight) of 1.20. As a result, it ispossible to confirm that the polymer chains grafted to the coreparticles have a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 5 wt. % of theelectrophoretic particles (white particles), 0.1 wt. % of a colorant(“Oil Blue N”, mfd. by Aldrich Co.), 2.5 wt. % of rosin acid (acidicadditive), and 92.9 wt. % of an electrophoretic dispersion medium(“Isoper H”, mfd. by Exxon Corp.). The electrophoretic particles arepositively charged by acid-base interaction between the grafted dodecylpolyacrylate and rosin acid. Further, the grafted dodecyl polyacrylatehas an expanse in the electrophoretic dispersion medium, thus havingalso a dispersion function.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 1(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearblue/white display.

EXAMPLE 2-2

A plurality of microcapsules 1 i each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 2-1 areprepared by in-situ polymerization method. Each microcapsule is formedof urea-formaldehyde resin as a film-forming material. Anelectrophoretic display device, as shown in FIG. 1(b), which isconnected with a voltage application circuit is prepared by disposingthe plurality of microcapsules 1 i on a first substrate 1 a by use ofnozzles according to the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles are excellent in dispersibility,chargeability, and (color) definition and it is possible to effect clearblue/white display.

EXAMPLE 2-3

In toluene, magnetite particles (average particle size: 200 nm, havinghydroxy group at particle surface) and Precursor 14 (n=6) of atomtransfer radical polymerization initiation group are reacted with eachother to introduce atom transfer radical polymerization initiation groupat the particle surface of magnetite particles. After the magnetiteparticles are dispersed in toluene, in the resultant system, octadecylmethacrylate is added. The reaction system is aerated with nitrogen andsubjected to atom transfer radical polymerization at 70° C. for apredetermined time. In this case, 2-bromo ethyl isobutylene as a freepolymerization initiation group (radical) is added in the reactionsystem in advance so as to provide an index of molecular weight andmolecular weight distribution of a polymer chain grafted to the particlesurface of magnetite particles.

After the polymerization, the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles 4 e.

The electrophoretic particles 4 e are well dispersed in chloroform, sothat it is possible to confirm that octadecyl polyacrylate is grafted atthe particle surface of magnetite. Further, when a polymer obtained from2-bromo ethyl isobutylate added as the free polymerization initiationgroup is subjected to measurement of molecular weight and molecularweight distribution, the polymer has a number-average molecular weightof about 110,000 and a molecular weight dispersion index (weight-averagemolecular weight/number-average molecular weight) of 1.07. As a result,it is possible to confirm that the polymer chains grafted to themagnetite particles have a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 1 wt. % of theelectrophoretic particles 4 e (black particles), 0.5 wt. % of rosin acid(acidic additive), and 98.5 wt. % of an electrophoretic dispersionmedium 4 f (“Isoper H”, mfd. by Exxon Corp.). The electrophoreticparticles 4 e are positively charged by acid-base interaction betweenthe grafted octadecyl polyacrylate and rosin acid. Further, the graftedoctadecyl polyacrylate has an expanse in the electrophoretic dispersionmedium 4 f, thus having also a dispersion function.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 4(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 2-4

A plurality of microcapsules 4 j each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 2-3 areprepared by interfacial polymerization method. Each microcapsule isformed of polyamide resin as a film-forming material. An electrophoreticdisplay device, as shown in FIG. 4(b), which is connected with a voltageapplication circuit is prepared by disposing the plurality ofmicrocapsules 4 j on a first substrate 4 a by use of nozzles accordingto the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,and chargeability, and it is possible to effect clear white/blackdisplay.

EXAMPLE 2-5

In toluene, magnetite particles (average particle size: 200 nm, havinghydroxy group at particle surface) and Precursor 5 (n=10) ofnitroxide-mediated polymerization initiation group are reacted with eachother to introduce nitroxide-mediated polymerization initiation group atthe particle surface of magnetite particles. After the magnetiteparticles are dispersed in dimethylformamide, in the resultant system,acrylic acid is added. The reaction system is aerated with nitrogen andsubjected to nitroxide-mediated polymerization at 100+ C. for apredetermined time. After acrylic acid is consumed, isoprene is added tothe reaction system in a molar ratio of (acrylic acid):(isoprene)=1:9 toform a graft polymer chain of block copolymer. In this case, nitroxidesimilar to Precursor 5 of the nitroxide-mediated polymerizationinitiation group as a free polymerization initiation group (radical) isadded in the reaction system in advance so as to provide an index ofmolecular weight and molecular weight distribution of a polymer chaingrafted to the particle surface of magnetite particles.

After the polymerization, the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles 4 e.

The electrophoretic particles 4 e are well dispersed in chloroform, sothat it is possible to confirm that block copolymer of polyacrylic acidand polyisoprene is grafted at the particle surface of magnetite.Further, when a polymer obtained from the nitroxide added as the freepolymerization initiation group is subjected to measurement of molecularweight and molecular weight distribution, the polymer has anumber-average molecular weight of about 70,000 and a molecular weightdispersion index (weight-average molecular weight/number-averagemolecular weight) of 1.28. As a result, it is possible to confirm thatthe polymer chains grafted to the magnetite particles are the blockcopolymer having a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 1 wt. % of theelectrophoretic particles 4 e (black particles), 0.5 wt. % ofpolyisobutylenesuccinimide (basic additive), and 98.5 wt. % of anelectrophoretic dispersion medium 4 f (“Isoper H”, mfd. by Exxon Corp.).The electrophoretic particles 4 e are positively charged by acid-baseinteraction between the grafted polyacrylic acid site of the blockcopolymer and polyisobutylenesuccinimide. Further, the graftedpolyisoprene site of the block copolymer has an expanse in theelectrophoretic dispersion medium 4 f, thus having a dispersionfunction.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 4(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 2-6

A plurality of microcapsules 4 j each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 2-5 areprepared by interfacial polymerization method. Each microcapsule isformed of polyamide resin as a film-forming material. An electrophoreticdisplay device, as shown in FIG. 4(b), which is connected with a voltageapplication circuit is prepared by disposing the plurality ofmicrocapsules 4 j on a first substrate 4 a by use of nozzles accordingto the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 1-7

In toluene, magnetite particles (average particle size: 100 nm, havinghydroxy group at particle surface) and Precursor 17 of atom transferradical polymerization initiation group are reacted with each other tointroduce atom transfer radical polymerization initiation group at theparticle surface of magnetite particles. After the magnetite particlesare dispersed in dimethylformamide, in the resultant system, aminoethylacrylate is added.

The reaction system is aerated with nitrogen and subjected to atomtransfer radical polymerization at 80° C. for a predetermined time.After aminoethyl acrylate is consumed, 1-hexene is added to the reactionsystem in a molar ratio of (aminoethyl acrylate):(1-hexene)=1:9 to forma graft polymer chain of block copolymer. In this case, benzyl chlorideas a free polymerization initiation group (radical) is added in thereaction system in advance so as to provide an index of molecular weightand molecular weight distribution of a polymer chain grafted to theparticle surface of magnetite particles.

After the polymerization, the resultant polymer particles are washed,followed by purification and drying to obtain objective electrophoreticparticles 4 e.

The electrophoretic particles 4 e are well dispersed in chloroform, sothat it is possible to confirm that block copolymer of polyacrylic acidand polyisoprene is grafted at the particle surface of magnetite.Further, when a polymer obtained from benzyl chloride added as the freepolymerization initiation group is subjected to measurement of molecularweight and molecular weight distribution, the polymer has anumber-average molecular weight of about 70,000 and a molecular weightdispersion index (weight-average molecular weight/number-averagemolecular weight) of 1.18. As a result, it is possible to confirm thatthe polymer chains grafted to the magnetite particles are the blockcopolymer having a uniform chain length.

An electrophoretic dispersion liquid is prepared by using 1 wt. % of theelectrophoretic particles 4 e (black particles), 0.5 wt. % of rosin acid(acidic additive), and 98.5 wt. % of an electrophoretic dispersionmedium 4 f (“Isoper H”, mfd. by Exxon Corp.). The electrophoreticparticles 4 e are positively charged by acid-base interaction betweenthe grafted polyaminoethyl acrylate site of the block copolymer andpolyisobutylenesuccinimide. Further, the grafted polyhexene site of theblock copolymer has an expanse in the electrophoretic dispersion medium4 f, thus having a dispersion function.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 4(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 2-8

A plurality of microcapsules 4 j each prepared in the same manner as inExample 2-7 are prepared by in-situ polymerization method. Eachmicrocapsule is formed of melamine-formaldehyde resin as a film-formingmaterial. An electrophoretic display device, as shown in FIG. 4(b),which is connected with a voltage application circuit is prepared bydisposing the plurality of microcapsules 4 j on a first substrate 4 a byuse of nozzles according to the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display for a long time by driving it at a drive voltage of ±10V, the electrophoretic particles 4 e are excellent in dispersibility,chargeability and (color) definition, and it is possible to effect clearwhite/black display.

EXAMPLE 2-9

An electrophoretic dispersion liquid is prepared by using 5 wt. % ofelectrophoretic particles (white particles) obtained in the same manneras in Example 2-1, 2.5 wt. % of rosin acid (acidic additive), 3 wt. % ofelectrophoretic particles (black particles) obtained in the same manneras in Example 2-5, 1.5 wt. % of polyisobutylenesuccinimide (basicadditive), and 88. wt. % of an EDM (Isoper H). In the electrophoreticdispersion liquid, the white electrophoretic particles are positivelycharged and the black electrophoretic particles are negatively charged.

The electrophoretic dispersion liquid is injected into a cell by usingnozzles according to an ink jet method to provide an electrophoreticdisplay device, as shown in FIG. 1(a), which is connected with a voltageapplication circuit.

When the resultant electrophoretic display device is subjected tocontrast display (FIG. 3) for a long time by driving it at a drivevoltage of ±10 V, the electrophoretic particles are excellent indispersibility, chargeability and (color) definition, and it is possibleto effect clear white/black display.

EXAMPLE 2-10

A plurality of microcapsules 1 i each containing an electrophoreticdispersion liquid prepared in the same manner as in Example 2-9 areprepared by in-situ polymerization method. Each microcapsule is formedof melamine-formaldehyde resin as a film-forming material. Anelectrophoretic display device, as shown in FIG. 1(b), which isconnected with a voltage application circuit is prepared by disposingthe plurality of microcapsules 1 i on a first substrate 1 a by use ofnozzles according to the ink jet method.

When the resultant electrophoretic display device is subjected tocontrast display (FIG. 3) for a long time by driving it at a drivevoltage of ±10 V, the electrophoretic particles are excellent indispersibility, chargeability and (color) definition, and it is possibleto effect clear white/black display.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Application Nos.161697/2004 filed May 31, 2004, and 171349/2004 filed Jun. 9, 2004,which are hereby incorporated by reference.

1. Electrophoretic particles comprising pigment particles, wherein at asurface of pigment particle, a polymer chain is connected with anitroxide-mediated polymerization initiation group.
 2. Electrophoreticparticles according to claim 1, wherein the polymer chain has amolecular weight distribution index (weight-average molecularweight/number-average molecular weight) of not more than 1.8.
 3. Anelectrophoretic display device, comprising: electrophoretic particlesaccording to claim 1, a dispersion medium for dispersing theelectrophoretic particles, and a cell in which the electrophoreticparticles and the dispersion medium are filled.
 4. A process forproducing electrophoretic particles comprising pigment particles,comprising: a step of introducing a nitroxide-mediated polymerizationinitiation group to a surface of pigment particle by reacting pigmentparticles having a function group, which is capable of reacting with aprecursor of the nitroxide-mediated polymerization initiation group,with the precursor of the nitroxide-mediated polymerization initiationgroup, and a step of grafting a polymer chain to the nitroxide-mediatedpolymerization initiation group by nitroxide-mediated polymerization. 5.A process according to claim 4, wherein the precursor of thenitroxide-mediated polymerization initiation group is triethoxysilylgroup, trimethoxysilyl group or trichlorosilyl group.
 6. A processaccording to claim 4 wherein the function group which is capable ofreacting with the precursor of the nitroxide-mediated polymerizationinitiation group is hydroxyl group.
 7. Electrophoretic particlescomprising pigment particles, wherein at a surface pigment particle, apolymer chain is connected with a living radical polymerizationinitiation group and the polymer has an affinity for a hydrocarbonsolvent.
 8. Electrophoretic particles according to claim 1, wherein thepolymer chain has a molecular weight distribution index (weight-averagemolecular weight/number-average molecular weight) of not more than 1.8.9. An electrophoretic display device, comprising: electrophoreticparticles according to claim 7, a dispersion medium containing ahydrocarbon solvent, and a cell in which the electrophoretic particlesand the dispersion medium are filled.
 10. A process for producingelectrophoretic particles comprising pigment particles, comprising: astep of forming a living radical polymerization initiation group at asurface of pigment particle, and a step of providing the pigmentparticles with a polymer chain connected with the living radicalpolymerization initiation group by living radical polymerization,wherein the polymer has an affinity for a hydrocarbon solvent.
 11. Aprocess for producing electrophoretic particles comprising pigmentparticles, comprising: a step of forming a nitroxide-mediatedpolymerization initiation group at a surface of pigment particle byreacting pigment particles each having hydroxyl group at a surfacethereof with a precursor of the nitroxide-mediated polymerizationinitiation group, and a step of polymerizing a monomer having anaffinity for a hydrocarbon solvent by nitroxide-mediated polymerizationand providing the pigment particles with the resultant polymer connectedwith the nitroxide-mediated polymerization initiation group.
 12. Aprocess for producing electrophoretic particles comprising pigmentparticles, comprising: a step of forming a atom transfer radicalpolymerization initiation group at a surface of pigment particle byreacting pigment particles each having hydroxyl group at a surfacethereof with a precursor of the atom transfer radical polymerizationinitiation group, and a step of polymerizing a monomer having anaffinity for a hydrocarbon solvent by atom transfer radicalpolymerization and providing the pigment particles with the resultantpolymer connected with the atom transfer radical polymerizationinitiation group.